Somebody should try out Magic Coat Kecleon. Of course, it'll take some prediction to bounce those status effects back at your opponent. Most of those sleepers tend to be Special based so 120 base Special Defense can't hurt either. There's always Trick Room to setup your teammates afterwards and it can hurt Milotic (Thunderbolt/Thunderpunch), Gengar (Shadow Ball/Shadow Sneak/Sucker Punch), Yanmega (Thunderbolt/Thunderpunch/Flamethrower/Fire Punch/Ice Beam/Ice Punch), etc. if they decide not to Sleep you.
kecleon @ Focus Sash
Magic Coat
Trick Room
Skill Swap
Shadow Claw
What about the synchrothiefing xatu from the D/P Analyses section?
name: Synchrothief
move 1: Thief
move 2: Psychic
move 3: Wish
move 4: Thunder Wave / Confuse Ray / Reflect / Light Screen / Tail Wind / U-turn / Psycho Shift
item: Lum Berry
ability: Synchronize
nature: Modest
evs: 252 hp/100 SpAtk/156 Spd
Open w/ something that doesn't like special conditions, then switch to this to synchro the condition, heal w/ lum, then thief their item. wish for healing and support, psychic for damage, then pick a good last move that helps support your team. tailwind seems interesting to set up some pokes w/ average speed to sweep. u-turn is a little more practical and helpful most of the time. psycho shift lets you take another non-sleep condition.
another possibility is early bird dodrio as a lead:
Dodrio @ Choice Band?/Life Orb?/Choice Scarf? (don't know what item since i don't play 3v3, maybe a half damage from ice/elec/rock berry?)
Pluck (could help against some berry users)
Brave Bird/Drill Peck
Pursuit
Mirror Move/Quick Attack (not w/ scarf)/Return/filler/double hit(in case you need to break subs. don't know if this is necessary)
could be an opener i suppose, 110 base attack + brave bird could do a lot. early bird reduces sleep count a lot. if you owuld have previously been asleep for 1 turn, it becomes 0 turns. 2-3 becomes 1 turn, 4-5 becomes 2 turns, etc. can pursuit against gengars etc. the threat of waking up instantly always exists, which in itself should be enough to keep people from attempting sleep. you could always switch it in rather than starting with it, but you might as well start with it i suppose, given its good power and somewhat versatile moveset.
from my 3v3 battling experience, which is not a lot, i have found this team to be fairly effective:
Breloom @ Toxic Orb
Poison Heal
Spore
Substitute
Focus Punch
Seed Bomb
100% sleep + amazing power and sub-punching skills makes him a decent opener.
Snorlax @ Leftovers
Immunity
Body Slam
Counter
Earthquake
Crunch
one of my fav pokes. switch into a special attack, hit whatever comes in, most likely a physical sweeper, or paralyze their special sweeper w/ body slam if they stay in. then counter their physical sweeper. as long as you survive the hit, you will almost always OHKO them, instantly destroying 1/3 of their team. also the 30% paralyze off body slam is amazingly helpful. has no counters due to crunch/earthquake. i love taking out ghosts who switch into body slam w/ a well-placed crunch.
Slowbro @ Leftovers/Sitrus Berry
Own Tempo
Surf
Ice Beam
Slack off
Calm Mind
Love this guy. He is one of my favorite walls. He can easily come in on a physical hit, calm mind once, and 1-2HKO them. If he comes in on a physical hit and calm minds once, then again on a special sweeper, he can absorb just about any hit, shrug it off w/ lefties and slack off, keep setting up calm minds, then sweep. leftover when no item clause applies. however, with item clause, sitrus helps a lot, turning 2HKOs to 3HKOs, 3 to 4, etc. allowing for time to slack off once then set up/sweep. assuming identical/no evs, his defensive capabilites are pretty much balanced after a single calm mind.
i really like this team becuase i have a sweeper, a special wall, and a physical wall, but both of my walls have decent attacking power as well.